It is known to provide an amplifier with a variable transconductance feedback network so that the gain of the amplifier can be varied in response to a control voltage applied to that network. Such arrangements are commonly used in automatic gain control circuits and in amplifiers with a programmable gain.
In a circuit which is constructed with MOS (metal-oxide semiconductor) technology, it is often difficult to obtain a variable transconductance network with a wide enough range of values for a sufficient range of gain control with essentially undistorted signal transmission. As a result, the circuit has a severely restricted range or requires too much power or chip area.